Process for short-time arc-welding and short-time arc-welding system

ABSTRACT

A process and a system are proposed for short-time arc-welding elements, such as for example metal studs, on to components, such as for example metal sheets, wherein an element in the context of a welding operation is initially raised in relation to the component, a welding arc is formed between the element and the component, and the element is lowered again, the lifting height of the element in relation to the component being detected at least within a time segment between raising and lowering of the element. The initiation of the lowering operation and/or the lowering operation itself is controlled as a factor of the detected lifting height such that a previously specified total welding time is achieved.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/763,123 filed on Jan. 22, 2004, which is a continuation of PCTapplication PCT/EP02/08130, filed on Jul. 22, 2002, which claimspriority to DE 101 36 991.3, filed on Jul. 23, 2001, all of which areincorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a process for short-time arc-weldingelements, such as for example metal studs, on to components, such as forexample metal sheets, wherein an element in the context of a weldingoperation is initially raised in relation to the component, a weldingarc is formed between the element and the component, and the element islowered again, the lifting height of the element in relation to thecomponent being detected at least within a time segment between raisingand lowering of the component.

The present invention further relates to a short-time arc-welding systemfor welding elements, such as for example metal studs, on to components,such as for example metal sheets, with a welding device which, in thecontext of a welding operation, initially raises an element in relationto the component and then lowers said element again, to a lifting heightdetection device to detect the lifting height of the element in relationto the component at least within a time segment between raising andlowering of the component, to a power supply device which provides thepower for forming an arc between the component and the raised element,and to a control device which triggers the welding device to raise andlower the element.

This process of short-time arc-welding or this short-time arc-weldingsystem respectively is also known generally by the term “stud welding”,for example from a brochure entitled “Die neue TUCKER-Technologie.Bolzenschweiβen mit System!” [“New TUCKER technology. The stud weldingsystem!”], published by Emhart TUCKER in September 1999.

The technology of stud welding is used in particular, but notexclusively, in automotive engineering. With this technology, studs withor without a thread, nuts, eyes and other elements can be welded on tobody panels. As a rule, the elements then serve as holding anchors forfastening interior trim elements, for example, to the vehicle body.

In the case of the above cited stud welding in accordance with TUCKER,an element is initially placed in a welding head. This can take placeusing an automatic feed device, for example by means of compressed air.By means of the welding head the element is now positioned at theappropriate point on the component. A pre-welding current is thenswitched on which flows through the stud and the component. The elementis then raised in relation to the component. An arc forms. The arc flowis selected such that initially contaminants, surface coatings such aszinc, oil or dry-film lubricants, etc. are burned off. The current thenswitches to a welding current. As a result of the high welding currentthe mutually opposing end faces of the element and component melt. Theelement is then lowered again on to the component so the mutual meltsare mixed. The welding current is switched off when the component isreached and the arc short-circuits. The melt solidifies and the weldjoint is complete.

In a generally known embodiment, the element is raised and lowered inrelation to the component takes place by means of an electromagnet or bymeans of a spring. To raise the element, the electromagnet is triggeredagainst the force of a compression spring. To lower the element, theelectromagnet is switched off and the energy stored in the springpresses the element against the component. In a more recent embodiment,the raising and lowering of the element in relation to the component areachieved by an electric motor, in particular by a linear motor. Thelinear motor is capable of driving along a predetermined lifting profileover time highly dynamically. In order to ensure that the specifiedlifting profile over time does not alter during operation, it is knownto measure the path of the linear motor and to return said path to forma closed loop.

From EP 0241 249 B1 (corresponding to DE-OS 36 11 823), it is known tomeasure the welding arc voltage and to control the welding currentprovided by means of a switched-mode power supply as a factor of thedetected arc voltage, it thus being possible to even out the weldingconditions varying from welding point to welding point and, despiteunfavorable circumstances, to achieve perfect welds. A fixed liftingcurve over time is predetermined for the lifting movements of theelement in relation to the component. A further short-time arc-weldingsystem is known from WO 96/10468. In this system the arc voltage duringthe welding operation is regulated to a desired value wherein thelifting height of the element in relation to the component is regulated.By this means it is possible not only to regulate the welding currentbut also the welding voltage during the welding operation, such thatpredetermined profiles of these parameters are repeatedly optimallyachieved over many welding operations. The lowering operation takesplace at a predetermined lowering speed and is initiated at a certainpoint in time. It has been shown that the above-mentioned knownshort-time arc-welding processes are still capable of improvement inrespect of consistency from welding operation to welding operation. Theobject of the present invention is to indicate an improved process ofshort-time arc-welding or an improved short-time arc-welding system,with which process or system, irrespective of the particular weldingconditions, optimal welding results are achieved. The object of theinvention is achieved in the case of the process of short-timearc-welding mentioned at the outset in that the initiation of thelowering operation and/or the lowering operation itself is controlled asa factor of the detected lifting height such that a previously specifiedtotal welding time is achieved. In the short-time arc-welding systemmentioned at the outset, the object of the invention is achieved in thatthe control device triggers the welding device in such a manner that theinitiation of the lowering operation and/or the lowering operationitself takes place as a factor of the lifting height reached such that apreviously specified total welding time is achieved. According to afurther aspect, this object in the case of the process of short-timearc-welding mentioned at the outset is achieved in that the initiationof the lowering operation and/or the lowering operation itself iscontrolled as a factor of the lifting height detected, such that apreviously specified total welding energy is achieved. The object of theinvention is fully achieved in this manner. In the case of systems, inparticular, wherein the lifting height during the welding operation isvariable, the present invention offers the advantage of a more evenquality of weld. In the case of the arc-welding process with regulationof the lifting height according to the prior art, owing to the fixedpoint in time of the initiation of the lowering operation and owing tothe fixed prescription of the lowering speed, different total weldingtimes may result. This can lead to different welding results from caseto case. By contrast, according to the invention the previouslyspecified total welding time is always reached constantly from case tocase, irrespective of the lifting height regulation curve. Altogether,more consistent welding results can be achieved in this manner despitedifferent boundary conditions (for example surface states).

In accordance with a further aspect of the invention, to achieve moreconsistent welding results there is no focus on a previously specifiedtotal welding time, but instead on a previously specified total weldingenergy, wherein the energy input into the welding operation ispredetermined and the point in time of initiation of the loweringoperation and/or the lowering operation itself are controlled as afactor of the detected lifting height such that the previously specifiedtotal welding energy is achieved.

The description hereinafter generally focuses on total welding time. Allreferences to total welding time, however, are also intended to referalternatively or cumulatively to the total welding energy. For example,it may be sensible to control the initiation of the lowering operationand/or the lowering operation itself as a factor of the detected liftingheight such that a previously specified combination of total weldingtime and total welding energy is achieved.

The present invention is also applicable to arc-welding processeswherein the lifting height is not regulated, but is controlled to avalue which is substantially constant. When using the welding processaccording to the invention, it is possible in this embodiment to achievea previously specified total welding time without necessitating theprescription of a specific trigger time for initiating the loweringoperation. Instead, the process according to the invention is used toachieve the previously specified total welding time by detecting thelifting height during the welding operation and controlling theinitiation of the lowering operation such that the previously specifiedtotal welding time is achieved. In a particularly preferred process thepoint in time of initiation of the lowering operation and/or thelowering speed is/are controlled as a factor of the detected liftingheight in order to achieve the previously specified total welding time.By means of these two parameters, the previously specified total weldingtime can be achieved in a comparatively simple manner in softwareengineering terms. It is especially preferred if the lowering speed isconstant irrespective of the lifting height and if the time ofinitiating the lowering operation is controlled as a factor of thelifting height in order to achieve the previously specified totalwelding time. In this embodiment the lowering speed can be selected suchthat, on the one hand, the lowering operation takes place rapidly enoughto prevent melt dripping from the underside of the element. On the otherhand, a speed can be selected that is sufficiently slow in order toprevent excessively rapid immersion in the melt of the component andthus rebounding. Depending on the actual lifting height during thewelding operation, the lowering operation is initiated such that thepreviously specified total welding time is achieved.

In accordance with an alternative embodiment, the lowering operation isinitiated at a previously specified time and the lowering speed iscontrolled in order to achieve the previously specified total weldingtime. This alternative embodiment is slightly easier to produce in termsof programming. The lowering speed is optionally variable, however,depending on the respective lifting height regulated during the weldingoperation. From the foregoing it is understood that the goal ofachieving a previously specified total welding time can also be achievedin that control of the initiation of the lowering operation and controlof the lowering operation itself (its speed) can be combined with oneanother.

Furthermore, it is also possible to control the lowering operationitself so as to control the acceleration of the lowering movement. Forexample, it may be sensible to lower the element at high speed directlyafter initiating the lowering operation and to reduce said speedgradually in order subsequently to achieve a comparatively gentleimmersion of the element in the melt of the component. Altogether it ispreferable if the lifting height during the welding operation isregulated at least until the lowering operation is initiated. It isespecially preferable if the regulation of the lifting height untilinitiation of the lowering operation serves to regulate the voltage ofthe welding arc to a constant value.

In the short-time arc-welding system according to the invention it isadvantageous if the welding device has an electric motor to raise andlower the element. Although generally the present invention is alsoapplicable to welding devices which use a combination of anelectromagnet and a spring for lifting movements of the element, the useof an electric motor is preferred because of the ease of regulatingelectric motors and the comparatively simply achieved dampingpossibilities. In this context it is of particular advantage if themotor is a linear motor. In this development, it is not necessary toprovide a rotational-translational converter to convert the rotationalmovements of the conventional electric motor into linear movements ofthe component. It is understood that the previously mentioned featuresand the features to be explained hereinafter can be used not only in therespectively indicated combination, but also in other combinations, orin isolation, without going beyond the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are represented in the drawings and areexplained in the description hereinafter. In the accompanying drawings:

FIG. 1 shows a schematic view of a short-time arc-welding systemaccording to the present invention;

FIG. 2 shows a diagram with a representation of the lifting height ofthe element, the welding current and the energy input during a weldingoperation over time in qualitative form;

FIG. 3 shows a representation of the lifting height corresponding toFIG. 2 when using the welding process according to the invention;

FIG. 4 shows a representation of the lifting height corresponding toFIG. 2 when using an alternative embodiment of the welding processaccording to the Invention; and

FIG. 5 shows a representation of the lifting height corresponding toFIG. 2 when using a further alternative embodiment of the weldingprocess according to the invention.

DETAILED DESCRIPTION

In FIG. 1 a short-time arc-welding system according to the invention isgenerally referred to by 10. The welding system 10 serves to weldelements such as metal studs 12 on to components such as metal sheets14. A typical practical example is the welding of fastening studs 12 onto the body panels 14 of motor vehicles. The elements concerned may bemetal studs with or without a thread, nuts, eyes, etc. The component 14may be a body panel, with sheet thicknesses as thin as 0.5 mm. Thewelding system 10 corresponds in its fundamental structure to theshort-time arc-welding system which is disclosed in the brochure “NeueTUCKER-Technologie. Bolzenschweiβen mit System!” [“New TUCKERtechnology. The stud welding system!”] mentioned at the outset. Theinformation disclosed in this brochure is implicit by reference. Thewelding system 10 has a control and energy unit 20 to which a pluralityof, typically five, feed units 22 can be connected. At least one weldinghead 24 is connected respectively to the feed units 22, of which feedunits 22 one is represented schematically in FIG. 1. The control andenergy unit 20 has a power supply device to form an arc between thecomponent 14 and the raised element 12. Further the control and energyunit has a main control device. The main control device serves, viasuitable interfaces, inter alia to input and display process parametersand to communicate with other processes, for example a production line.The control and energy unit 20 has an interface 26 for the purpose ofcommunicating with other processes. The feed units 22 serve to isolateand to reliably feed elements such as metal studs 12 to the welding head24, said feed units 22 each having an isolating device, a pneumaticportion for conveying isolated elements to the welding head 24, and afeed control device.

The welding head 24 receives from the feed unit 22 one element 12 to bewelded at a time. For this purpose the welding head 24 has a holderknown per se (not shown in detail). Further a linear motor 28 isprovided in order to move the holder—and with the holder the element12—in a direction roughly perpendicular to the component 14 on a linearpath, as is shown schematically at 29. Consequently by means of theelectric linear motor 28 the height H of the element 12 can be adjustedin relation to the component 14 (lifting height). Further the weldinghead 24 has a lifting height detection means 30 which detects therespective actual lifting height H. In FIG. 1 the connections betweenthe control and energy unit 20 and the feed unit 22 and between the feedunit 22 and the welding head 24 are shown respectively as a single line.However, it is understood that these connections each containcommunication lines for the exchange of information and for transmittingcontrol commands between the control devices of the control and energyunit 20, of the respective feed units 22 and of the respective weldingheads 24.

Further the connections contain power supply lines for supplying thewelding head 24 with power from the power supply device of the controland energy unit 20. The connection further contains a compressed airline between the feed unit 22 and the welding head 24, which compressedair line is for feeding elements 12 that are to be welded on. Whenproviding a distributing guide (not illustrated), two or optionally evenmore welding heads 24 may be connected to one feed unit 22. The weldingheads 24 may be permanently mountable welding heads which, for example,are attached permanently to a robot arm, or else may be freelymanipulatable welding guns. The feed units 22 and the welding heads 24can respectively be adapted to fit different kinds of elements 12, bothin respect of the material characteristics (for example, steel oraluminum studs) and in respect of the form (Christmas tree studs,earthing studs, threaded studs, etc.).

The welding system 10 as shown represents only one preferred embodimentfor use in the industrial field. It is understood that other embodimentscould be designed without a special feed unit, the elements 12 to bewelded on then being placed in a holder by hand. The operation of thewelding system 10 is explained generally hereinafter by reference toFIG. 2. FIG. 2 shows, applied over time t, the lifting height H of theelement 12 in relation to the component 14, the welding current I, whichcurrent flows from the control and energy unit 20 via the feed unit 22and the welding head 24 through the stud 12 and the component 14, andthe energy quantity E applied to the weld joint. The representation ofthese variables is of purely qualitative and schematic nature in orderto simplify explanation thereof.

When carrying out a weld, initially the element 12 is placed on thecomponent 14 so that an electrical contact is formed. Subsequently at apoint in time t₁ a so-called pre-current I_(v) is switched on. Shortlythereafter, at a point in time t₂, the element 12 is raised in relationto the component 14, until a point in time t₃ at which the welding liftheight is reached. During this time the pre-current remains switched on.An arc is drawn as the element 12 is raised. The pre-current arc hassufficient energy to burn off contaminants present in the region of thewelding point or to evaporate possible layers of wax. After reaching thewelding lift height, at time t₄, the welding current I_(s) is broughtinto circuit. As a result of the high welding current I_(s) ofapproximately, 20 A to 1,500 A for example, the element 12 and thecomponent 14 are melted in the region of the drawn arc. The energy Eflowing into the welding operation increases. The lowering operation isinitiated at a point in time t₅. The element 12 is lowered at apredetermined speed until at a time t₆ it impinges on the component 14.At this point in time, the arc is short-circuited and the weldingcurrent I_(s) is switched off. As shown qualitatively in FIG. 2, thelowering operation can take place until slightly below the zero line, inorder to guarantee a saturated immersion of the element 12 in the meltedsurface of the component 14. The melts of element 12 and component 14unite and cool down owing to the interruption in the energy input. Thetotal energy quantity applied is designated by E_(end) in FIG. 2. Theelement 12 is thus welded firmly on to the component 14 and may serve asan anchor for fixing parts to the component 14. In FIG. 2 the totalwelding time T_(s) is shown, i.e. the time from t₄ to t₆. Thepre-current time T_(v) is represented as the time from t₁ to t₄. Finallya lowering time T_(A) is visible, being the time from t₅ to t₆. Thewelding operation described by reference to FIG. 2 corresponds to theprior art. To raise and lower the element 12, either a linear motor or aspring-mass system (with an electromagnet and counter spring) can beused.

In particular when using the electric linear motor 28, the liftingheight H can be regulated by setting a certain desired profile for thelifting action and causing the measured lifting height H to be regulatedto the respective desired profile. This makes it possible to obtain anaccurate positional definition between the element 12 and the component14 at each point in time of the welding operation. The current I is madeavailable from a constant-current source from the power supply device ofthe control and energy unit 20. The arc voltage between the element 12and the component 14 consequently is adjusted according to theelectrical resistance present between these two elements. The electricalresistance depends decisively on the surface characteristics,contaminants, etc. and can vary from welding operation to weldingoperation.

From the WO 96/10468 mentioned at the outset, it is therefore known toregulate the lifting height H during the welding operation such that thearc voltage between the element 12 and the component 14 is constant orfollows a predetermined finished profile. By means of this system it ispossible to maintain the arc voltage constant during the weldingoperation and thereby to obtain smaller fluctuations in welding qualityfrom welding operation to welding operation. Details of the regulationprocess are disclosed in WO 96/10468, the disclosure of which herein isfully implicit by reference thereto. In this document it is alsodescribed that the lowering operation takes place at a certain loweringspeed which is set beforehand.

In the prior art, this can mean that the total welding time T_(s) variesfrom welding operation to welding operation. If, for example, in therepresentation in FIG. 2 the lifting height H at the time t₅ is greaterthan that shown, the time t₆ will shift backwards in time because thelowering speed is constant. Consequently the total welding time T_(s)will also be lengthened. If by contrast the lifting height is less thanthat shown in FIG. 2 at the time t₅ owing to the regulation of thelifting height for adjusting the arc voltage, the time t₆ will shiftforwards in time, which leads to a shortening of the total welding timeT_(s). It is understood that the energy input E will also altercorrespondingly depending on lifting height H at time t₅.

A preferred embodiment of the arc-welding process according to theinvention is shown in FIG. 3. In FIG. 3, on the one hand, the profile ofthe lifting height H is presented as reference, as is also shown in FIG.2. In order to obtain a constant total welding time T_(s), withotherwise unchanged boundary conditions, the welding operation isterminated at t₆, irrespective of the lifting height H last adjustedduring the welding operation owing to closed-loop control. If theelement 12 for arc voltage regulation is raised, for example, in thecourse of the welding operation, as is shown schematically at H′,subject to a constant lowering speed, the initiation of the loweringoperation will already take place at a time t₅′ which lies prior to thepoint in time t₅. If, in contrast, during the regulation a lower liftingheight is set, as is shown schematically at H″, the lowering operationwill only be initiated at a point in time t₅″, which lieschronologically after the point in time t₅.

The maintenance of a constant lowering speed starting from theinitiation of the lowering operation until the point in time t₆ has thefollowing advantages. The lowering speed can, on the one hand, be chosento be high enough in order to prevent melt dripping from the element 12on to the component 14 before immersion. On the other hand, the loweringspeed can be selected to be sufficiently slow in order to prevent a hardimpact on the component 14 which impact could lead to a rebounding andsplashing of melt. The value of the set predetermined lowering speed inthe case of this embodiment is consequently a compromise between thesetwo boundary conditions.

FIG. 3 further shows that the welding process according to the inventioncan also be used if the lifting height H is not regulated. However, itmay be that in different instances different lifting heights are desiredduring the welding operation, as shown in FIG. 3 by H, on the one hand,and by H′″, on the other hand. Conventionally, a different shutdown timet₅ or t₅′″ respectively would have to be programmed for the variouslifting heights H and H′″. In the process according to the invention,the correct point in time t₅ or t₅′″ selected automatically by means ofthe detected lifting height, thereby rendering a special programming ofthis point in time unnecessary.

FIG. 4 shows an alternative embodiment of the welding process accordingto the invention. In this embodiment the regulation of the liftingheight is always up to a fixed point in time t₅, irrespective of thelifting height H_(a) or H_(b) present at the time t₅. In ordernevertheless to achieve a set predetermined total welding time, thespeed of the lowering operation is selected such that the loweringoperation always terminates at a point in time t₆. In the example shownin FIG. 4 the lifting height on the curve H_(a) is thus relatively highat the point in time t₅. Consequently a relatively high speed must beset in order to terminate the total welding operation at the point intime t₆. If, on the other hand, the lifting height at the point in timet₅ is relatively low, as is shown on curve H_(b), the speed to beselected to reach the total welding duration will be relatively low.

This alternative embodiment of the process according to the invention isslightly simpler to program. In contrast, the embodiment of FIG. 3 hasthe advantage of a uniform lowering speed and thus a defined immersionoperation. A further embodiment of the process according to theinvention is presented in FIG. 5. In this embodiment, similarly to theembodiment in FIG. 4, the regulation of lifting height during thewelding operation always takes place by the point in time t₅.

In order subsequently to achieve a constant total welding time T_(s),not only is there action to influence the speed of the loweringoperation, but also to influence the acceleration thereof. Thus by meansof the course of the lifting height action H_(x) it can be detected, forexample, that directly after the point in time t₅ the lifting height isreduced initially at a relatively high speed and the speed whileapproaching the point in time t₆ is continuously reduced in order toachieve a gentle immersion operation. It is understood that this mannerof influencing the lowering operation can also be used with theembodiment in FIG. 3, in that, instead of a continuous lowering speed, acertain path-time profile of the lowering operation is predetermined,which path-time profile, for example, can take on the form of aparabola, as is shown in FIG. 5.

In FIG. 5 a further lifting curve H_(y) is shown wherein the loweringoperation is also initiated at a point in time t₅ and is terminated at apoint in time t₆. In this embodiment, to achieve an especially hardimpact on the component 14 the lifting height after initiating thelowering operation at the point in time t₅ is still maintainedcomparatively high, and, while approaching the point in time t₆, theelement 12 is then accelerated towards the component 14.

It is understood that the embodiments in FIGS. 3, 4 and 5 can also bemutually combined in order to complete a welding operation with acertain total welding duration and/or a certain total welding energy.Furthermore it is understood that the process according to the inventioncan also be applied to short-time arc-welding processes in which the arcis not “drawn”.

1. A process for welding an element to a component using a feed unit and a welding head, the process comprising: (a) feeding the element from the feed unit to the welding head; (b) lifting the element along a substantially linear path in relation to the component; (c) detecting a height that the element was lifted; (d) energizing the welding head; (e) welding the element to the component for a specified welding energy; (f) lowering the element in relation to the component; and (f) stopping energy to the welding head upon completion of the specified welding energy, wherein the specified welding energy is controlled by a speed lowering the element, wherein the speed is controlled as a function of at least the height.
 2. The process of claim 1 wherein the component is a body panel for a motor vehicle.
 3. The process of claim 2 wherein thickness of the body panel is about 0.5 mm.
 4. The process of claim 1 further comprising continually detecting the height during substantially an entirety of the specified welding energy.
 5. The process of claim 4 further comprising initiating the lowering the element toward the component while holding the arc-welding at a constant electrical voltage based on the detected height.
 6. The process of claim 1 wherein the element is a metal stud.
 7. The process of claim 1 wherein the component is a metal sheet.
 8. The process of claim 1 further comprising controlling a speed of the lowering as a factor of a speed of the lifting the element along a substantially linear path.
 9. The process of claim 1 wherein the speed of lowering decreases as the distance of the element relative to the component decreases.
 10. The process of claim 1 further comprising maintaining the height until the initiation of the lowering.
 11. A process for controlling welding of an element to a component by a welder, the process comprising: (a) determining an energizing height; (b) retracting the element to a height; (c) energizing the welder at the energizing height to create a welding arc; (d) welding the element to the component for a specified welding energy; (e) advancing the element in relation to the component; (f) detecting the height as the element and component are welded together; and (g) de-energizing the welder at end of the specified welding energy.
 12. The process of claim 11 wherein the element is a metal stud and the component is a metal sheet.
 13. The process of claim 12 wherein the metal stud and the metal sheet are parts of a motor vehicle.
 14. The process of claim 11 wherein an advancing speed is constant regardless of a retracting speed.
 15. The process of claim 11 wherein the specified welding energy is controlled by a speed of the advancing the element.
 16. The process of claim 11 wherein the energizing height is maintained until the initiation of the advancing the element.
 17. The process of claim 11 wherein a speed of the advancing the element is controlled as a factor of a speed of the retracting.
 18. The process of claim 11 further comprising feeding the element into the welder.
 19. A process for welding an element to a component using a feed unit and welding head, the process comprising: (a) feeding the element from the feed unit to the welding head; (b) moving the element along a substantially linear path from the component to a first location; (c) detecting a distance that the element was moved; (d) energizing the welding head; (e) welding the element to the component for a specified welding energy; (f) lowering the element relative to the component; and (g) stopping energy to the welding head at an end of the specified welding energy, wherein the specified welding energy is controlled by a speed lowering the element, wherein the speed is controlled as a function of at least the distance.
 20. The process of claim 19 wherein the component is a body panel.
 21. The process of claim 20 wherein thickness of the body panel is about 0.5 mm.
 22. The process of claim 20 wherein the body panel is part of a motor vehicle.
 23. The process of claim 19 further comprising continually detecting the distance during substantially an entirety of the specified welding energy.
 24. The process of claim 23 further comprising initiating lowering the element toward the component while holding the arc-welding at a constant electrical voltage is based on the detected distance.
 25. The process of claim 19 wherein the element is a metal stud.
 26. The process of claim 19 further comprising maintaining the distance until the initiation of the lowering of the element. 